Re: [PATCH] drm/bridge: tc358767: Expose test mode functionality via debugfs

From: Andrey Smirnov
Date: Tue Aug 27 2019 - 18:52:12 EST

On Tue, Aug 27, 2019 at 1:06 AM Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Andrey,
>
> On Mon, Aug 26, 2019 at 09:24:57PM -0700, Andrey Smirnov wrote:
> > On Mon, Aug 26, 2019 at 3:08 PM Laurent Pinchart wrote:
> > > On Mon, Aug 26, 2019 at 11:25:24AM -0700, Andrey Smirnov wrote:
> > > > Presently, the driver code artificially limits test pattern mode to a
> > > > single pattern with fixed color selection. It being a kernel module
> > > > parameter makes switching "test patter" <-> "proper output" modes
> > > > on-the-fly clunky and outright impossible if the driver is built into
> > > > the kernel.
> > > >
> > > > To improve the situation a bit, convert current test pattern code to
> > > > use debugfs instead by exposing "TestCtl" register. This way old
> > > > "tc_test_pattern=1" functionality can be emulated via:
> > > >
> > > > echo -n 0x78146312 > tstctl
> > > >
> > > > and switch back to regular mode can be done with:
> > > >
> > > > echo -n 0x78146310 > tstctl
> > >
> > > Can't we make this more userfriendly by exposing either a test pattern
> > > index, or a string ?
> >
> > We could, but then a) it would require more code in the driver b) the
> > files wouldn't correspond directly to something described in the
> > part's datasheet. Just didn't seem worth it to me.
>
> Could you then provide me with the datasheet ? :-)

Is this a rhetoric question or are you seriously asking? If its the
latter I can ping you off the list.

> The whole point of a
> driver is to avoid needing detailed knowledge of the device's internals
> in userspace.
>

You won't avoid needing detailed knowledge of the device's internals
if you don't have a priori knowledge in the form of a agreed upon/well
known abstraction you are exposing from the driver. There is no such
abstraction in this case. Whether you present "tstctl" that takes a
magic value or "red", "green", "blue" and "pattern" taking numbers and
special strings, as a user, you still would have to go read the driver
code in order to figure out how that stuff works.

Given how this is an obscure _debug_ feature for a niche part, I think
exposing raw register and leaving a comment in the driver source code
explaining how it works is reasonably user-friendly (for all 10 - 15
unique users that this feature would ever have).

To avoid any further back and forth of this subject, how about the
following. If this is up to me, then I'd like to move forward to v2
with the interface as is. If you feel strongly about this and insist
on your vision of the interface, please let me know what it looks like
(e.g. is what I described above good enough) and I'll rework v2 to
have that.

> > > Do all bits in the register need to be controlled
> > > from userspace ?
> >
> > Pretty much, yes. It's formatted as RR_GG_BB_X_M, where R, G, B
> > specifies color used for various patterns, X is irrelevant and M
> > specifies test pattern to use.
> >
> > > > Note that switching to any of the test patterns, will NOT trigger link
> > > > re-establishment whereas switching to normal operation WILL. This is
> > > > done so:
> > > >
> > > > a) we can isolate and verify (e)DP link functionality by switching to
> > > > one of the test patters
> > > >
> > > > b) trigger a link re-establishment by switching back to normal mode
> > > >
> > > > Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
> > > > Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> > > > Cc: Laurent Pinchart <Laurent.pinchart@xxxxxxxxxxxxxxxx>
> > > > Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
> > > > Cc: Cory Tusar <cory.tusar@xxxxxxxx>
> > > > Cc: Chris Healy <cphealy@xxxxxxxxx>
> > > > Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> > > > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > > ---
> > > > drivers/gpu/drm/bridge/tc358767.c | 137 ++++++++++++++++++++++--------
> > > > 1 file changed, 101 insertions(+), 36 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c
> > > > index 6308d93ad91d..7a795b613ed0 100644
> > > > --- a/drivers/gpu/drm/bridge/tc358767.c
> > > > +++ b/drivers/gpu/drm/bridge/tc358767.c
> > > > @@ -17,6 +17,7 @@
> > > >
> > > > #include <linux/bitfield.h>
> > > > #include <linux/clk.h>
> > > > +#include <linux/debugfs.h>
> > > > #include <linux/device.h>
> > > > #include <linux/gpio/consumer.h>
> > > > #include <linux/i2c.h>
> > > > @@ -222,11 +223,10 @@
> > > > #define COLOR_B GENMASK(15, 8)
> > > > #define ENI2CFILTER BIT(4)
> > > > #define COLOR_BAR_MODE GENMASK(1, 0)
> > > > +#define COLOR_BAR_MODE_NORMAL 0
> > > > #define COLOR_BAR_MODE_BARS 2
> > > > -#define PLL_DBG 0x0a04
> > > >
> > > > -static bool tc_test_pattern;
> > > > -module_param_named(test, tc_test_pattern, bool, 0644);
> > >
> > > I assume that his being a debug feature there's no system relying on the
> > > module parameter that would break if you remove it ?
> >
> > Yeah, I don't know of any system that needs that parameter. It seems
> > pretty useless for anything but basic debugging.
> >
> > > > +#define PLL_DBG 0x0a04
> > > >
> > > > struct tc_edp_link {
> > > > struct drm_dp_link base;
> > > > @@ -789,16 +789,6 @@ static int tc_set_video_mode(struct tc_data *tc,
> > > > if (ret)
> > > > return ret;
> > > >
> > > > - /* Test pattern settings */
> > > > - ret = regmap_write(tc->regmap, TSTCTL,
> > > > - FIELD_PREP(COLOR_R, 120) |
> > > > - FIELD_PREP(COLOR_G, 20) |
> > > > - FIELD_PREP(COLOR_B, 99) |
> > > > - ENI2CFILTER |
> > > > - FIELD_PREP(COLOR_BAR_MODE, COLOR_BAR_MODE_BARS));
> > > > - if (ret)
> > > > - return ret;
> > > > -
> > > > /* DP Main Stream Attributes */
> > > > vid_sync_dly = hsync_len + left_margin + mode->hdisplay;
> > > > ret = regmap_write(tc->regmap, DP0_VIDSYNCDELAY,
> > > > @@ -1150,14 +1140,6 @@ static int tc_stream_enable(struct tc_data *tc)
> > > >
> > > > dev_dbg(tc->dev, "enable video stream\n");
> > > >
> > > > - /* PXL PLL setup */
> > > > - if (tc_test_pattern) {
> > > > - ret = tc_pxl_pll_en(tc, clk_get_rate(tc->refclk),
> > > > - 1000 * tc->mode.clock);
> > > > - if (ret)
> > > > - return ret;
> > > > - }
> > > > -
> > > > ret = tc_set_video_mode(tc, &tc->mode);
> > > > if (ret)
> > > > return ret;
> > > > @@ -1186,12 +1168,8 @@ static int tc_stream_enable(struct tc_data *tc)
> > > > if (ret)
> > > > return ret;
> > > > /* Set input interface */
> > > > - value = DP0_AUDSRC_NO_INPUT;
> > > > - if (tc_test_pattern)
> > > > - value |= DP0_VIDSRC_COLOR_BAR;
> > > > - else
> > > > - value |= DP0_VIDSRC_DPI_RX;
> > > > - ret = regmap_write(tc->regmap, SYSCTRL, value);
> > > > + ret = regmap_write(tc->regmap, SYSCTRL,
> > > > + DP0_AUDSRC_NO_INPUT | DP0_VIDSRC_DPI_RX);
> > > > if (ret)
> > > > return ret;
> > > >
> > > > @@ -1220,39 +1198,44 @@ static void tc_bridge_pre_enable(struct drm_bridge *bridge)
> > > > drm_panel_prepare(tc->panel);
> > > > }
> > > >
> > > > -static void tc_bridge_enable(struct drm_bridge *bridge)
> > > > +static int __tc_bridge_enable(struct tc_data *tc)
> > > > {
> > > > - struct tc_data *tc = bridge_to_tc(bridge);
> > > > int ret;
> > > >
> > > > ret = tc_get_display_props(tc);
> > > > if (ret < 0) {
> > > > dev_err(tc->dev, "failed to read display props: %d\n", ret);
> > > > - return;
> > > > + return ret;
> > > > }
> > > >
> > > > ret = tc_main_link_enable(tc);
> > > > if (ret < 0) {
> > > > dev_err(tc->dev, "main link enable error: %d\n", ret);
> > > > - return;
> > > > + return ret;
> > > > }
> > > >
> > > > ret = tc_stream_enable(tc);
> > > > if (ret < 0) {
> > > > dev_err(tc->dev, "main link stream start error: %d\n", ret);
> > > > tc_main_link_disable(tc);
> > > > - return;
> > > > }
> > > >
> > > > - drm_panel_enable(tc->panel);
> > > > + return ret;
> > > > }
> > > >
> > > > -static void tc_bridge_disable(struct drm_bridge *bridge)
> > > > +static void tc_bridge_enable(struct drm_bridge *bridge)
> > > > {
> > > > struct tc_data *tc = bridge_to_tc(bridge);
> > > > - int ret;
> > > >
> > > > - drm_panel_disable(tc->panel);
> > > > + if (__tc_bridge_enable(tc) < 0)
> > > > + return;
> > > > +
> > > > + drm_panel_enable(tc->panel);
> > > > +}
> > > > +
> > > > +static int __tc_bridge_disable(struct tc_data *tc)
> > > > +{
> > > > + int ret;
> > > >
> > > > ret = tc_stream_disable(tc);
> > > > if (ret < 0)
> > > > @@ -1261,6 +1244,16 @@ static void tc_bridge_disable(struct drm_bridge *bridge)
> > > > ret = tc_main_link_disable(tc);
> > > > if (ret < 0)
> > > > dev_err(tc->dev, "main link disable error: %d\n", ret);
> > > > +
> > > > + return ret;
> > > > +}
> > > > +
> > > > +static void tc_bridge_disable(struct drm_bridge *bridge)
> > > > +{
> > > > + struct tc_data *tc = bridge_to_tc(bridge);
> > > > +
> > > > + drm_panel_disable(tc->panel);
> > > > + __tc_bridge_disable(tc);
> > > > }
> > > >
> > > > static void tc_bridge_post_disable(struct drm_bridge *bridge)
> > > > @@ -1372,6 +1365,77 @@ static enum drm_connector_status tc_connector_detect(struct drm_connector *conne
> > > > return connector_status_disconnected;
> > > > }
> > > >
> > > > +static int tc_tstctl_set(void *data, u64 val)
> > > > +{
> > > > + struct tc_data *tc = data;
> > > > + int ret;
> > > > +
> > > > + if (FIELD_GET(COLOR_BAR_MODE, val) == COLOR_BAR_MODE_NORMAL) {
> > > > + ret = regmap_write(tc->regmap, SYSCTRL, DP0_VIDSRC_DPI_RX);
> > > > + if (ret) {
> > > > + dev_err(tc->dev,
> > > > + "failed to select dpi video stream\n");
> > > > + return ret;
> > > > + }
> > > > +
> > > > + ret = regmap_write(tc->regmap, TSTCTL, val | ENI2CFILTER);
> > > > + if (ret) {
> > > > + dev_err(tc->dev, "failed to set TSTCTL\n");
> > > > + return ret;
> > > > + }
> > > > +
> > > > + ret = tc_pxl_pll_dis(tc);
> > > > + if (ret) {
> > > > + dev_err(tc->dev, "failed to disable PLL\n");
> > > > + return ret;
> > > > + }
> > > > +
> > > > + /*
> > > > + * Re-establish DP link
> > > > + */
> > > > + ret = __tc_bridge_disable(tc);
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + ret = __tc_bridge_enable(tc);
> > > > + if (ret)
> > > > + return ret;
> > >
> > > If the bridge is currently disabled you should not enable it. I think
> > > you need to guard against race conditions with the enable/disable
> > > functions, as well as delay writes until the bridge gets enabled if it
> > > is currently disabled.
> >
> > OK, will do in v2.
> >
> > > > + } else {
> > > > + ret = tc_pxl_pll_en(tc, clk_get_rate(tc->refclk),
> > > > + 1000 * tc->mode.clock);
> > > > + if (ret) {
> > > > + dev_err(tc->dev, "failed to enable PLL\n");
> > > > + return ret;
> > > > + }
> > > > +
> > > > + ret = regmap_write(tc->regmap, TSTCTL, val | ENI2CFILTER);
> > > > + if (ret) {
> > > > + dev_err(tc->dev, "failed to set TSTCTL\n");
> > > > + return ret;
> > > > + }
> > > > +
> > > > + ret = regmap_write(tc->regmap, SYSCTRL, DP0_VIDSRC_COLOR_BAR);
> > > > + if (ret) {
> > > > + dev_err(tc->dev, "failed to color bar video stream\n");
> > > > + return ret;
> > > > + }
> > > > + }
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +DEFINE_SIMPLE_ATTRIBUTE(tc_tstctl_fops, NULL, tc_tstctl_set, "%llu\n");
> > >
> > > Shouldn't you also provide a get handler ?
> >
> > There really isn't a use-case for reading the value of TestCtl AFAICT,
> > so, I skipped it to avoid having extra code.
> >
> > > > +static int tc_late_register(struct drm_connector *connector)
> > > > +{
> > > > + if (connector->debugfs_entry)
> > > > + debugfs_create_file_unsafe("tstctl", 0644,
> > > > + connector->debugfs_entry,
> > > > + connector_to_tc(connector),
> > > > + &tc_tstctl_fops);
> > > > + return 0;
> > > > +}
> > >
> > > Why a .late_register() handler, can't you do this at probe time ?
> >
> > .late_register() happens after drm_debugfs_connector_add() where
> > connector->debugfs_entry gets initialized. AFAICT, I could move that
> > code to probe, but then I'd have create a separate debugfs root
> > directory as well as add code to clean it up (currently I rely on
> > drm_debugfs_connector_remove() removing everything recursively.
>
> The usual approach for this kind of debug feature is to create a
> directory named after dev_name() in order to guarantee uniqueness. I
> feel that could be better, but have no strong preference.
>

Sure, I can move it to probe in v2.

Thanks,
Andrey Smirnov